In the long-term evolution infrastructure, user equipment (UE) can be in one of two radio resource control states. These are LTE_IDLE and LTE_ACTIVE.
The UE can be configured for discontinuous reception (DRX) in both the LTE_IDLE and the LTE_ACTIVE states. In the LTE_IDLE state, the DRX allows the UE to synchronize its listening period to a known paging cycle of the network. By synchronizing the listening period, the UE can turn off its radio transceiver during the standby period, thereby significantly saving battery resources. DRX parameters allow the mobile to synchronize with the network and to know that it will not receive another signal until a specified time has elapsed.
It is proposed at the 3GPP TSG-RAN working groups that DRX also be used when the UE is LTE-ACTIVE state. An issue with this is handover response.
During the DRX awake period, the UE is triggered to send a measurement report (MR) in accordance with rules that it receives from radio resource control (RRC) messages, system information blocks, among others.
In operation, a source enhanced node B (eNB) makes a handover initiation decision based on the measurement report and radio resource management information to hand off the user equipment to a target eNB. This handover initiation decision is made before the source eNB sends the handover request to the target eNB. The handover request is then sent to the target eNB. The target eNB performs admission control dependent on the received bearer quality of service (QoS) information and loading conditions. If the resources can be granted by the target eNB, it configures them according to the received bearer QoS information and reserves the appropriate resources.
The target eNB sends the handover request acknowledgement to the source eNB. The handover request acknowledgement includes a transparent container to send to the UE as part of the handover command. The source eNB then sends the handover command to the UE when the UE next gets out of its DRX sleep period.
Based on the current DRX operation during handover, the handover command could be delayed due to the DRX sleep period, which may cause longer handover latency.